This invention relates to polymer gels and membranes. In particular it relates to polymer gels and membranes that are suitable for separation of molecules. The invention is also concerned with the preparation of novel polymer gels and membranes, the separation of molecules by techniques such as electrophoresis using these gels and membranes, and crosslinking agents useful in their preparation. The invention also relates to polymer gels of interest in areas that include bio-compatible applications such as prosthetic devices and optical and eye lenses.
The invention is especially suitable for electrophoretic applications and accordingly, for convenience, the invention will be further described with reference to electrophoresis. It is to be understood, however, that the gels, membranes, processes and crosslinking agents of the present invention are not so limited.
Polyacrylamide gels used for electrophoresis are conventionally prepared by the copolymerization of the acrylamide (AAm) with methylene-bis-acrylamide (BIS) as the crosslinker (Scheme 1). 
Such polyacrylamide gels have a number of limitations in electrophoretic applications, such as a limited porosity range1, high background silver staining2, low resistance to hydrolysis when stored in alkaline media, and restriction to concentration of the gel solution due to the lack of clarity.
Since both double bonds of BIS are of the same type, their reactivities are essentially the same. We have previously found an improvement in the separation of polyacrylamide gels when they are prepared using particular asymmetrical crosslinking agents (see PCT/AU97/00437, the disclosure of which is incorporated herein by reference).
We have now discovered that using multifunctional crosslinkers, that is crosslinkers having at least three crosslinkable functional groups, gives some unexpected improved properties. These improvements include:
1) Greater control when designing gels with a different pore size range;
2) Control of pore size distribution;
3) Greater resistance to hydrolysis in alkaline media;
4) Greater clarity of gels prepared with high concentration of the crosslinkers;
5) Reduced background after silver staining.
Accordingly, in one aspect, the present invention provides a crosslinked polymer gel formed from a least one monomer and at least one crosslinker having at least three crosslinkable functional groups, wherein at least one of the crosslinkable functional groups is an acryloyl or methacryloyl group as hereinafter defined.
The said at least three crosslinkable functional groups of the crosslinker may be the same or different.
The crosslinker may be a linear, branched or cyclic compound. Preferably all functional groups of the crosslinker have an ethylenic double bond. More preferably, the crosslinker has at least three acryloyl functional or methacryloyl groups or a combination thereof. Preferably, each acryloyl or methacryloyl group is attached to a nitrogen or oxygen atom.
The crosslinked polymer gel may be formed in the presence of one or more conventional crosslinker(s).
The monomer or monomers used to prepare the gel may be any suitable monomer. The gel may be formed from two or more different monomers.
The crosslinked polymer gel may be prepared from one or more monomers having the formula H2C=CR5xe2x80x94COxe2x80x94NR3R4 where R3, R4 are each independently H, alkyl, alcohol (xe2x80x94(CH2)axe2x80x94OH), or ester (xe2x80x94(CH2)axe2x80x94OCH3), where n is 1-6, and R5 is H or optionally substituted alkyl. Examples of monomers include acrylamide, acrylamide derivatives or acrylamide substitutes known to the art such as N,N-dimethylacrylamide, methacrylamide, N-methyloylacrylamide, propylacrylamide, dipropyl acrylamide, isopropyl acrylamide, diisopropyl acrylamide, lactyl acrylamide, methoxyacrylamide and mixtures thereof. Preferably the, or at least one of, the monomer(s) is acrylamide.
In a preferred form of the invention, the crosslinker used in the crosslinked polymer gel of the invention is a compound selected from Formula I and/or Formula II 
wherein, in Formula I:
C represents a ring structure of the crosslinker molecule which is connected with at least 3 functional groups xe2x80x94Yxe2x80x94CZC(R)xe2x95x90CH2 which functional groups may be the same or different;
Y in each functional group may be the same or different and selected from a single bond, N, O or S;
Z in each functional group may be the same or different and selected from O or S; or Z may be two hydrogens, a hydrogen and an optionally substituted alkyl, or two optionally substituted alkyl groups; and
R in each functional group may be the same or different and selected from hydrogen or substituted or unsubstituted alkyl, preferably H or CH3.
Ring C may be a 3 to 12-membered carboxyclic or heterocyclic ring. Preferably C is a six-membered heterocyclic ring. The heteroatom)s) in the heterocyclic ring may be independently selected from N, O or S. Examples of suitable ring structures include heterocyclic amines and oxides. Y in each functional group may be the same or different and selected from N, O or S when it is connected to a carbon atom that is part of the ring system. Y may be a single bond if the functional group is connected to a ring nitrogen.
Preferably, each functional group is connected to the ring C through a heteroatom. Preferably the heteroatom is N. The heteroatom may be a ring atom or a heteroatom of a ring C substituent.
Ring C may be a heterocyclic nitrogen-containing ring, for example, a ring having the structure: 
In Formula II:
D represents a backbone chain of the crosslinker which is connected with at lest three functional groups xe2x80x94Yxe2x80x94CzC(R)xe2x95x90CH2 which functional groups may be the same or different;
Y in each functional group may be the same or different and selected from a single bond, N, O or S;
Z in each functional group may be the same or different and selected from O or S; and
R in each functional group may be the same or different and selected from hydrogen or substituted or unsubstituted alkyl, preferably H or CH3.
The backbone chain of the compound of Formula II may be linear, branched or cyclic. The backbone may optionally be substituted and/or optionally interrupted by one or more heteroatoms O, S, N and/or one or more aromatic, saturated or unsaturated carboxyclic or heterocyclic radicals. The backbone may be a small molecule (monomer), oligomer or polymer. Y in each functional group may be the same or different and selected from N, O or S if the backbone chain contains only carbons. Y may also be a single bond if the backbone chain contains N within the chain or contains N or O or S at the ends of the main backbone chain or a branched chain to connect with the functional groups.
Preferably, each functional group is connected to the backbone via a heteroatom. Preferably, the heteroatom is N. The heteroatom may be a heteroatom interrupting the backbone, a heteroatom at the end(s) of the backbone chain, or it may be a heteroatom of a branching group of the backbone chain.
The backbone chain may be a relatively small molecule of sufficient length to allow substitution of 3 to about 6 crosslinkable functional groups.
The backbone chain may be a linear, branched or cyclic oligomer having approximately 3-20 repeat units, which may be the same or different. Examples of suitable oligomer backbones are polyalkylene imine oligomers (eg polyethylene imine oligomers) and polyalkylene oxides oligomers.
The backbone chain of the compound of formula II may be a linear, branched or cyclic polymer having a length up to about one million atoms. The polymer may be a polyalkylene imine (eg polyethylene imine) or polyalkylene oxide. The polymer may have a degree of substitution of up to 100% of the functional group.
The term xe2x80x9cacryloylxe2x80x9d as used herein denotes the group CH2xe2x95x90CHxe2x80x94COxe2x80x94 and;
The term xe2x80x9cmethacryloylxe2x80x9d as used herein denotes the group CH2xe2x95x90C(R)xe2x80x94COxe2x80x94, where R is optionally substituted alkyl, preferably C1-C4 alkyl, more preferably CH3 .
In this specification the term xe2x80x9coptionally substitutedxe2x80x9d means that a group may or may not be further substituted with one or more groups selected from alkyl, cycloalkyl, alkenyl, alkynyl, halo, haloalkyl, haloalkynyl, hydroxy, alkoxy, alkenyloxy, haloalkoxy, haloalkenyloxy, nitro, amino, nitroalkyl, nitroalkenyl, nitroalkynyl, nitroheterocyclyl, alkylamino, dialkylamino, alkenylamine, alkynylamino, acyl, alkenacyl, alkynylacyl, acylamino, diacylamino, acyloxy, alkylsulphonyloxy, heterocyclyl, heterocycloxy, heterocyclamino, haloheterocyclyl, alkylsulphenyl, carboalkoxy, alkylthio, acylthio, phosphorous-containing groups such as phosphono and phosphinyl.
The term xe2x80x9calkylxe2x80x9d, used either alone or in compound words such as xe2x80x9chaloalkylxe2x80x9d or xe2x80x9calkylthioxe2x80x9d, denotes straight chain or branched C1-6 alkyl groups. Examples include methyl, ethyl, propyl, isopropyl and the like.
The term xe2x80x9calkoxyxe2x80x9d denotes straight chain or branched alkoxy, preferably C1-10 alkoxy. Examples include methoxy, ethoxy, n-propoxy, isopropoxy and the different butoxy isomers.
The term xe2x80x9calkenylxe2x80x9d denotes groups formed from straight chain, branched or monoxe2x80x94or polycyclic alkenes including ethylenically monoxe2x80x94or polyxe2x80x94unsaturated alkyl or cycloalkyl groups as previously defined, preferably C2-10 alkenyl. Examples of alkenyl include vinyl, allyl, 1-methylvinyl, butenyl, iso-butenyl, 3-methyl-2-butenyl, 1-pentenyl, cyclopentenyl, 1-methyl-cyclopentenyl, 1-hexenyl, 3-hexenyl, cyclohexenyl, 1-heptenyl, 3-heptenyl, 1-octenyl, cyclooctenyl, 1-nonenyl, 2-nonenyl, 3-nonenyl, 1-decenyl, 3-decenyl, 1,3-butadienyl, 1-4,pentadienyl, 1,3-cyclopentadienyl, 1,3-hexadienyl, 1,4-hexadienyl, 1,3-cyclohexadienyl, 1,4-cyclohexadienyl, 1,3-cycloheptadienyl, 1,3,5-cycloheptatrienyl, or 1,3,5,7-cyclooctatetraenyl.
The term xe2x80x9chalogenxe2x80x9d denotes fluorine, chlorine, bromine or iodine, preferably chlorine or fluorine.
The term xe2x80x9cacylxe2x80x9d used either alone or in compound words such as xe2x80x9cacyloxyxe2x80x9d, xe2x80x9cacylthioxe2x80x9d, xe2x80x9cacylaminoxe2x80x9d or xe2x80x9cdiacylaminoxe2x80x9d denotes carbamoyl, aliphatic acyl group and acyl group containing a heterocyclic ring which is referred to as heterocyclic acyl, preferably C1-10 acyl. Examples of acyl include carbamoyl; straight chain or branched alkanoyl, such as formyl, acetyl, propanoyl, butanoyl, 2-methylpropanoyl, pentanoyl, 2,2-dimethylpropanoyl, hexanoyl, heptanoyl, octanoyl, nonanoyl, decanoyl; alkoxycarbonyl, such as methoxycarbonyl, ethoxycarbonyl, t-butoxycarbonyl, t-pentyloxycarbonyl or heptyloxycarbonyl; cycloalkylcarbonyl such as cyclopropylcarbonyl cyclobutylcarbonyl, cyclopentylcarbonyl or cyclohexylcarbonyl; alkylsulfonyl, such as methylsulfonyl or ethylsulfonyl, alkoxysulfonyl, such as methoxysulfonyl or ethoxysulfonyl; heterocyclycarbonyl; heterocyclylalkanoyl, such as pyrrolidinylacetyl, pyrrolidinylpropanoyl, pyrrolidinylbutanoyl, pyrrolidinylpentanoyl, pyrrolidinylhexanoyl or thiazolidinylacetyl; heterocyclylalkenoyl, such as heterocyclylpropenoyl, heterocyclylbutenoyl, heterocyclylpentenoyl or heterocyclylhexenoyl; or heterocyclylglyoxyloyl, such as, thiazolidinylglyoxyloyl or pyrrolidinylglyoxyloyl.
An example of a compound of Formula I is compound 1. 
wherein R1, R2 and R3, which may be the same or different, are selected from H or optionally substituted alkyl.
An example of a compound of Formula II is compound 2. 
wherein R4, R5 and R6, which may be the same or different, are selected from H or optionally substituted alkyl and p is 1 to about 6.
A further example of a compound of Formula II is 
wherein n represents the number of repeating unit of the polyethylene imine backbone and m represents the number of acryloyl or methacryloyl groups substituted on the backbone, m and n being at least 3.
The polymer gel according to this invention may be an electrophoresis gel, which may or may not have a porosity gradient or composition gradient. The gradient may be achieved by using different concentrations of the polymer gel or by altering the ratio of crosslinker to monomer.
The electrophoresis gel may have a porosity gradient suitable for gradient gel electrophoresis. See for example, Polyacrylaminde Gel Electrophoresis across a Molecular Sieve Gradient Margolis, J., Kenrick, K. G., Nature, 214, 1967, p 1334-1336; Polyacrylamide Gel Electrophoresis in a Continuous Molecular Sieve Gradient, Margolis, J., Kenrick, K. G., Analytical biochemistry, 25, 1968, p347-362and Practical System for Polyacrylamide Gradient Gel electrophoresis, Margolis, J., Laboratory Practice, 22, p107-109, 1973, the disclosures of which are incorporated herein by reference.
The polymer gel of the present invention may be in the from of a membrane.
Accordingly, in a further aspect the present invention provides an electrophoretic membrane including an electrophoretic gel in accordance with the present invention formed on a porous substrate.
The substrate may have a larger pore size than that of the electrophoretic medium. The substrate may be a porous paper or fabric. The substrate may be woven or non-woven sheet, for example, a non-woven PET.
The greater control on designing gels with a different pore size range and/or distribution provided by the polymer gels of the present invention make them particularly suitable for use in electrophoresis separation method and apparatus described in Gradipore Limites""s U.S. Pat. No. 5,039,386 and U.S. Pat. No. 5,650,055, the disclosures of which are incorporated herein in their entirety. This technology is incorporated into Gradipore Limited""s Grandiflow(trademark) technology. The technology allows for the separation of macromolecules such as proteins, nucleotides and complex sugars. It can be used for size separation, concentration and dialysis. A commercially available form of this technology is Grandipore Limited""s Babyflow(trademark) BF200 unit. The hear of Gradiflow(trademark) is a membrane cartridge, which consists of three polyacrylamide-based membranes. The top and bottom membranes are small pore size restriction membranes. These membranes allow the movement of small ions, The middle membrane is the separating membrane, which varies with the particular application. This middle membrane usually has a larger, but defined pore size. It is in this middle membrane that the membrane of the present invention may have particular application. For specific applications, the membrane may be charged or have an affinity ligand embedded within the membrane.
In yet a further aspect of the present invention, there is provided a method of preparing a crosslinked polymer gel, said method including the step of subjecting one or more monomers to crosslinking polymerization in the presence of one or more crosslinking agents of Formula I and/or Formula II set out above.
The method of the present may be carried out in the presence of one or more other crosslinkers conventionally used in the art.
Preferable polymerizations are carried out in a solution of the monomer or monomers with the crosslinking agent(s). For most applications involving polyacrylamide gels, the solvent will be water. However, other solvents including DMF, THF, alcohol and other water miscible systems may be required.
The polymer gels according to this invention may be useful for separating molecules, especially charged species, or species capable of bearing a charge such as bio-molecules.
Accordingly, in a further aspect, the invention provides a method of separating molecules including:
providing a crosslinker polymer gel by combing one or more monomers with a crosslinker of Formula I and/or Formula II, optionally with one or more other crosslinker(s), subjecting the monomer solution to polymerization and crosslinking, in the presence of an initiator, placing a sample containing the molecules to be separated onto the gel, and subjecting the gel and sample to a separation technique.
The polymerization may be initiated by well known means such as UV, photopolymerization, redox or thermal initiation systems.
The present invention is not limited to obtaining a crosslinked polymer gel using a free radical polymerization method. The double bonds of the crosslinkers can be crosslinked with each other to form gels in other non radical polymerization reactions such as the xe2x80x98Michael additionxe2x80x99. The Michael addition involves a conjugate addition between a nucleophile such as a diamine with an xcex1,xcex2-unsaturated carbonyl such as the double bond of an acryloyl or methancryloyl group. One or more crosslinking agents of Formula I and/or Formula II and/or in the presence of one or more other crosslinkers conventionally used in the art, with or without a nucleophile possessing two or more reactive nucleophilic groups. A nucleophile can be a diamine NH2xe2x80x94(R)axe2x80x94NH2 where R in each diamine is a CH2 group and n is between 1-10 and can produce a 3-gel network as shown in scheme 2. Furthermore, the crosslinking agent of Formula I and/or Formula II can undergo self crosslinking reactions under the Michael addition conditions, where the NH2 group on the crosslinker acts as the nucleophile (scheme 3). 
Preferably the separation technique is electrophoresis.
The electrophoresis technique employed may be any of those known to the art, including onexe2x80x94, twoxe2x80x94and multi-dimensional techniques. The electrophoresis technique may be gradient gel electrophoresis.
The separation technique may be that described in Gradipore Limited""s U.S. Pat. No. 5,039,386 and U.S. Pat. No. 5,650,055.
The molecule separated using the separation method of the invention may be a bio-molecule. The term xe2x80x9cbio-moleculexe2x80x9d as herein denotes biological molecules such as proteins, enzymes and other peptides, genetic material such as chromosomal material, genomic DNA, cDNA, mRNA, tRNA and other oligoxe2x80x94and polynucleotides. The term includes naturally occurring biological molecules in addition to fragments and recombinant derivatives thereof.
The polymerization reaction between the monomers according to this invention is generally a free radical reaction, carried out in an aqueous medium, which can be initiated by any known initiator system, including initiator and co-initiator. Suitable free radical providing initiator systems include peroxides, such as benzoyl peroxide with or without a co-initiator; various persulfates, such as ammonium persulfate (APS); or azo-compounds such as azodiiosobutyronitrile. Typical co-initiators when APS is used are amine such as N,N,N1,N1-tetramethylethylenediamine (TEMED) or dimethylaminopropionitrile (DMAPN). The polymerization may also be initiated by photo-polymerization, UV or thermal initiation systems.
The gels according to this invention may include conventional additives known to the art as required by the techniques employed. These additives include, but are not limited to, detergents, for example, sodium dodecyl sulphate (SDS); denaturing agents, for example, urea; high molecular weight polymers, such as linear polyacrylamide; an low molecular weight species, such as glycerols, polyethylene glycol, polysaccharides, agarose and cellulose triacetates. The gel may also include a suitable buffer system.
In still a further aspect, the present invention provides a method for preparing a polymer gel having one or more preselected properties, the method including combining one or more monomers with a crosslinker of Formula I and/or Formula II, optionally with one or more other crosslinker(s), optionally in the presence of an initiator, and subjecting the monomer(s) and crosslinker(s) to polymerization and crosslinking, wherein the nature and/or amount of the crosslinker of Formula I and/or Formula II is selected to produce a gel having said one or more preselected property(ies).
The preselected property of properties may be selected from one or more of:
1) pore size range;
2) pore size distribution;
3) resistance to hydrolysis in alkaline media;
4) clarity, of gels (eg by using high concentration of the crosslinker(s); and
5) Reduced background after silver staining.
The preselected property e.g. porosity, may be achieved by varying the number and/or type of functional groups present on the crosslinker and/or the structure of the crosslinker (eg, linear, cyclic or branched). The preselected property may be achieved by using a combination of two or more different crosslinking agents in accordance with the present invention, the crosslinking agents differing in their backbone and/or ring and/or their functional groups. Some specific examples of these various combinations are given below:
A crosslinked polymer gel formed from at least one crosslinker and optionally at least one monomer, wherein the at least one crosslinker has at least three functional groups CH2xe2x95x90C(R)xe2x80x94COxe2x80x94, where R is H or CH3, wherein at least one functional group is attached to a nitrogen and at least one other functional group is attached to a heteroatom other than nitrogen.
A crosslinked polymer gel formed from a mixture of crosslinkers and optionally at least one monomer, wherein the mixture of crosslinkers comprises (a) at least one crosslinker having at least three functional groups CH2xe2x95x90CHxe2x80x94COxe2x80x94 each attached to a nitrogen and (b) at least one crosslinker having at least three functional groups CH2xe2x95x90C(CH3)xe2x80x94Cxe2x80x94 each attached to a nitrogen.
A crosslinked polymer gel formed from a mixture of crosslinkers and optionally at least one monomer, wherein the mixture of crosslinkers comprises (a) at least one crosslinker having at least three functional groups CH2xe2x95x90CHxe2x80x94COxe2x80x94, wherein at least one functional group CH2xe2x95x90CHxe2x80x94COxe2x80x94 is attached to a nitrogen and at least one other functional group CH2xe2x95x90CHxe2x80x94COxe2x80x94is attached to a heteroatom other than nitrogen and (b) at least one crosslinker having at least three functional groups CH2xe2x95x90C(CH3)xe2x80x94COxe2x80x94, wherein at least one of functional groups CH2xe2x95x90C(CH3)xe2x80x94COxe2x80x94 is attached to a nitrogen and at least one other functional group CH2xe2x95x90C(CH3)xe2x80x94COxe2x80x94 is attached to a heteroatom other than nitrogen.
A crosslinked polymer gel formed from a mixture of crosslinkers and optionally at least one monomer, wherein the mixture of crosslinkers comprises (a) at least one crosslinker having at least three functional groups CH2xe2x95x90CHxe2x80x94COxe2x80x94, wherein each functional group CH2xe2x95x90CHxe2x80x94COxe2x80x94 is attached to a nitrogen and (b) at least one crosslinker having at least three functional groups CH2xe2x95x90C(CH3)xe2x80x94COxe2x80x94 wherein at least one of functional groups CH2xe2x95x90C(CH3)xe2x80x94COxe2x80x94 is attached to a nitrogen and at least one other functional group CH2xe2x95x90C(CH3)xe2x80x94COxe2x80x94 is attached to a heteroatom other than nitrogen.
A crosslinked polymer gel formed from a mixture of crosslinkers and optionally at least one monomer, wherein the mixture of crosslinkers comprises (a) at least one crosslinker having at least three functional groups CH2xe2x95x90CHxe2x80x94COxe2x80x94, wherein at least one functional group CH2xe2x95x90CHxe2x80x94COxe2x80x94 is attached to a nitrogen and at least one other functional group CH2xe2x95x90CHxe2x80x94COxe2x80x94 is attached to a heteroatom other than nitrogen and (b) at least one crosslinker having at least three functional groups CH2xe2x95x90C(CH3)xe2x80x94COxe2x80x94, wherein each functional groups CH2xe2x95x90C(CH3)xe2x80x94COxe2x80x94 is attached to a nitrogen.
The polymer gel of the present invention may have a larger pore size compared to that of polymer gels prepared using the conventional AAm/BIS system. Moreover the polymer gel of the invention may have a high surface area of the polymer network and a capability of absorbing more solvents.
In yet a further aspect the present invention provides novel compounds suitable for use as crosslinkers, the compounds being accordance with Formula I or Formual II: 
wherein, in Formula I:
C represents a ring structure of the crosslinker molecule which is connected with at least 3 functional groups xe2x80x94Yxe2x80x94CZC(R)xe2x95x90CH2 which functional groups may be the same or different;
Y in each functional group may be the same or different and selected from single bond, N, O or S;
Z in each functional group may be the same or different and selected from O or S; or Z may be two hydrogens, a hydrogen an optionally substituted alkyl, or tow optionally substituted alkyl groups; and
R in each functional group may be the same or different and selected from hydrogen or optionally substituted alkyl, preferably H or CH3, but excluding the compounds hexamethylenetriamine triacrylate and hexamethylenetriamine trimethacrylate.
Ring C may be a 3 to 12-membered carboxyclic or heterocyclic ring. Preferably C is a six-membered heterocyclic ring. The heteroatom(s) in the heterocyclic ring may be independently selected from N, O or S. Examples of suitable ring structures include heterocyclic amines and oxides. Y in each functional group may be the same or different and selected from N, O or S when it is connected to a carbon atom that is part of the ring system. Y may be a single bond if the functional group is connected to ring nitrogen.
Ring C may be heterocyclic nitrogen containing ring, for example, a ring having the structure: 
In Formula II:
D represents a backbone chain of the crosslinker which is connected with at lest three functional groups xe2x80x94Yxe2x80x94CZC(R)xe2x95x90CH2 which functional groups may be the same or different;
Y in each functional group may be the same or different and selected from a single bond, N, O or S;
Z in each functional group may be the same or different and selected from O or S; and
R in each functional group may be the same or different and selected from hydrogen or optionally substituted alkyl, preferably H or CH3.
The backbone chain of the compound of Formula II may be linear, branched or cyclic. The backbone may optionally be substituted and/or optionally interrupted by one or more heteroatoms O,S,N and/or one or more aromatic, saturated or unsaturated carbocylic or heterocyclic radicals. The backbone may be a small molecule (monomer), oligomer or polymer. Y in each functional group may be the same or different and selected from N, O or S if the backbone chain contains only carbons. Y may also be a single bond if the backbone chain contains N or O or S at the ends of the main backbone chain or a branched chain to connect with the functional groups.
Preferably, each functional group is connected to the backbone via a heteroatom. Preferably, the heteroatom is N. The heteroatom may be a heteroatom interrupting the backbone or it may be a heteroatom of a branching group of the backbone chain.
The backbone chain may be a small molecule of sufficient length to allow substitution of 3 to about 6 crosslinkable functional groups.
The backbone chain may be a linear, branched or cyclic oligomer having approximately 3-20 repeat units, which may be the same or different. Examples of suitable oligomer backbones are polyalkyleneimine oligomers (eg polyethyleneimine oligomers) and polyalkylene oxides oligomers.
The backbone chain of the compound of formula II may be a linear, branched or cyclic polymer having a length up to about a million atoms. The polymer may be a polyalkyleneimine (eg polyethyleneimine) or polyalkylene oxide. The polymer may have a degree of substitution of up to about 80% of the functional groups.
Particularly preferred compounds of Formula II of the invention are trimethacyloyldiethylenetriamine, triacryloyl-tris(2-aminoethyl)amine, trimethacryloyl-tris(2-aminoethyl)amine and multi-acryloyl-substituted polyethyleneimines of the formula 
wherein n represents the number of repeating unit of the polyethylene imine backbone and m represents the number of acryloyl or methacryloyl groups substituted on the backbone, m and n being at least 3.
The crosslinking agents according to this invention may be prepared by conventional methods. The number and amount of the functional groups, which may be similar or different, may be introduced on the same crosslinker, depending on the size of the molecules to be separated. The synthesis methodologies described below are particularly preferred and the present invention extends to these methods of synthesis.
The relative amount of the crosslinker to the monomer may be about 2-15%C but may vary from this amount depending on the desired properties of the gel formed.
The crosslinkers of the present invention have application in crosslinking of polymers other than polymer gels and accordingly in yet a further aspect, the present invention provides a crosslinked polymer formed from at least one monomer and at least one crosslinker having at least three crosslinkable functional groups, wherein at least one of the crosslinkable functional groups is an acryloyl group.
The following examples are provided for the purpose of further illustration of the present invention but are in no way to be taken as limiting the scope of the present invention.